This proposal is aimed at 1) understanding the relationship between identified elements within the motor cortical network and locomotion behavior, and 2) understanding the mechanisms governing thalamo-cortical relations in the intact, functioning motor system. All data will be obtained from cats trained to walk inside an experimental chamber on a flat surface at different speeds, uphill and downhill, with weights attached to forelimbs, overcoming obstacles and walking on flat cross-pieces of a horizontal ladder. The relationship of identified cortico-cortical neurons, corticofugal efferent neurons and putative interneurons will be recorded during different locomotion behaviors. In addition, the activity of these identified neurons will be recorded simultaneously with the activity of thalamo-cortical projection neurons, and interactions among them will be analyzed using cross correlation methods at " rest" and during locomotion. Special emphasis will be placed on elucidating rules governing the strength and specificity of functional connections among the population of thalamo-cortical and cortical neurons under study. Two major issues will be addressed: 1) To what extent does the activity of different classes of identified motor cortex efferent neurons (e.g., S1, SII, collosal, corticothalamic, corticospinal, etc) and putative inhibitory interneurons differ in relation to locomotion under different conditions? Are properties better associated with cortical layer, morphological cell type or the destination of the axon? 2) What are the activity patterns of VL thalamo-cortical projection neurons during locomotion under different conditions and how do these patterns compare with those of cortical neurons? What are the characteristics of the synaptic linkages between VL projection neurons and cortical recipient neurons and how do these linkages change under different conditions of locomotion?